The present invention relates to lubricating oil compositions. More particularly, the present invention relates to lubricating oil compositions, which are designed for use with four cycle outboard marine engines.
The invention embodies new oil blends specifically formulated for use in four cycle outboard engines. These oils are differentiated from crankcase oils by a high phosphorus level. These oils also contain a molybdenum antioxidant/antiwear additive and a rust inhibitor additive.
Current practice for four cycle outboard oils is to use heavy duty diesel oils. This technology was never designed to meet the specific performance needs of four cycle outboard engines. The oils embodied in this invention provide specific performance improvements desirable in four cycle outboard engines: improved antioxidancy, antiwear, rust inhibition, shear stability, good water tolerance, air entrainment and high temperature foam properties.
In accordance with the invention, there is provided a lubricating oil composition for use in four cycle outboard marine engines, which composition comprises at least one oil of lubricating viscosity, an ashless dispersant, a metal detergent, at least one molybdenum compound in an amount sufficient to provide the composition with 15 to 1,000 ppm by mass, of molybdenum, an amount of ZDDP (zinc dialkyldithiophosphate) that contributes at least 1,200 ppm of phosphorus to the lubricating oil composition, an effective amount of a rust inhibitor and, optionally, a viscosity modifier, the lubricating oil composition having a NOACK volatility of 15 wt. % or less.
A further embodiment of this invention comprises a method of operating and lubricating a four cycle outboard marine engine which comprises supplying to said engine the lubricating oil composition of this invention.